The present invention relates to a molding apparatus, and more particularly, to a molding apparatus for making a continuous molded article.
Foam-in-place packaging is a highly useful technique for on-demand protection of packaged products. In its most basic form, foam-in-place packaging comprises injecting foamable compositions from a dispenser into a container that holds a product to be cushioned. Typically, the product is wrapped in plastic to keep it from direct contact with the rising (expanding) foam. As the foam rises, it expands into the remaining space between the product and its container (e.g. a box formed of corrugated paperboard), thus forming a custom cushion for the product.
A common foaming composition is formed by mixing an isocyanate compound with a hydroxyl-containing material, such as a polyol (i.e., a compound that contains multiple hydroxyl groups), typically in the presence of water and a catalyst. The isocyanate and polyol precursors react to form polyurethane. At the same time, the water reacts with the isocyanate compound to produce carbon dioxide. The carbon dioxide causes the polyurethane to expand into a foamed cellular structure, i.e., a polyurethane foam, which serves to protect the packaged product.
In other types of foam-in-place packaging, the foam precursors are injected into a plastic bag, which is then dropped into a container holding the product to be cushioned. The rising foam again tends to expand into the available space, but does so inside the bag. Because the bags are formed of flexible plastic, they form individual custom foam cushions for the packaged products. In several techniques, a specific apparatus is used to make the bag from plastic film while concurrently injecting it with foam. Exemplary devices for making such ‘foam-in-bag’ packaging cushions are assigned to the assignee of the present invention, and are illustrated, for example, in U.S. Pat. Nos. 5,027,583, 5,376,219, and 6,003,288, the contents of each of which are hereby incorporated entirely herein by reference thereto.
In other packaging applications, similar or identical products are repeatedly placed in similar or identical orientations in similar or identically sized containers. Such circumstances increase the need for more standard packaging elements that have a consistent size and shape.
U.S. Pat. Nos. 5,776,510, 6,386,850, and 7,607,911, the contents of each of which are hereby incorporated entirely herein by reference thereto, disclose methods and apparatus for automatically molding defined three-dimensional polyurethane foam cushions utilizing the foam-in-bag techniques discussed above, but with the added feature of placing a bag containing a foamable composition in a mold as the composition begins to form foam, and maintaining the bag in the mold until the composition has finished forming a foam cushion in a shape conforming to the shape of the mold. These inventions have beneficially combined the advantages of on-demand, foam-in-bag packaging with the ability to produce standard packaging cushions having a consistent size and shape.
While the forgoing molding techniques have been highly successful, the inventors hereof have determined that for high-volume molding applications, a molding apparatus capable of making a continuous molded article, e.g., which may be separated into a series of foam-in-bag molded cushions, would be highly beneficial. One approach for making a continuous molded, foamed article, or a series thereof, is to employ a pair of spaced-apart molding assemblies, e.g., comprising a pair of counter-rotating endless belts, which drive a series of movable mold segments that align and converge to form a movable mold with a dynamic mold cavity therein. A dispenser of a moldable, expandable composition, e.g., a polyurethane foam composition as described above, may further be employed to dispense the composition into the dynamic mold-cavity on a continuous basis, with a film-feeding mechanism also employed to continuously feed a center-folded film, or a pair of films, into the dynamic mold-cavity, such that the film is interposed between the moldable composition and the molding assemblies.
A significant difficulty with the foregoing approach is that the dynamic nature of the process makes it difficult to maintain a consistent mold-cavity shape. In order for the dynamic mold-cavity to form a desired mold shape, the movable mold segments must maintain a predetermined alignment as they are conveyed along a path in each molding assembly. However, after the initial introduction of the expandable, e.g., foamable, composition into the dynamic mold-cavity, the composition expands as it hardens into a foam. Such expansion and hardening occurs as the composition is conveyed within the dynamic mold-cavity, the shape of which must be maintained by the moving mold segments as the expanding foam exerts a force against such segments, due to physical contact therebetween. The magnitude of the force increases as the foam expands to fully fill the cavity, due to the increased area of contact in the mold-cavity between the expanding foam and the moving mold segments.
As may be appreciated, certain directional components of the expanding foam-force, e.g., in the direction along which the segments are being conveyed, has a tendency to cause the mold segments to deviate from their predetermined alignment, i.e., to push the mold segments out of alignment during their conveyance along the moving mold path. This tendency exists because of the dynamic nature of the continuous molding process—since the mold segments are movable, they can be moved not only in the direction of conveyance, which is desired, but can also be moved out of their mold-shape alignment, which is highly undesirable because such misalignment results in a poorly-formed molded article at best, and a catastrophic failure of the molding assembly at worst.
Another difficulty associated with the foregoing continuous molding process concerns proper alignment of both the foam dispensing device and sealing equipment used to seal the foam inside the film, vis-à-vis the dynamic mold-cavity. By changing the mold segments, the shape of the mold-cavity can be changed to produce molded articles having a desired shape. Such changes in the mold shape often necessitate the ability to inject the foam at different positions, e.g., to coincide with the widest or deepest part of the mold-cavity, and/or to seal the film at variable positions.
A further difficulty of continuous molding pertains to the release of the mold segments from the molded article at the end of the dynamic mold-cavity. With an endless-belt type molding assembly, for example, the mold segments diverge in a rotational fashion from the mold-cavity at a rotary guide member. Depending on the shape of the molded article, such release can be difficult to accomplish without causing damage to the molded article.
Accordingly, there remains a need in the art for improvements in the machines and processes for making a continuous series of molded articles, which overcome the foregoing difficulties.